Polymer latices of high viscosity



United States Patent 3,401,134 POLYMER LATICES OF HIGH VISCOSITY JoelFantl, Frank J. Hahn, and John F. Heaps, Springfield, and Charles R.Williams, Longmeadow, Mass, assignors to lVIonsanto Company, St. Louis,Mo., a corporation of Delaware No Drawing. Continuation-impart ofapplication Ser. No. 161,301, Dec. 21, 1961. This application Sept. 24,1964, Ser. No. 399,062

The portion of the term of the patent subsequent to Jan. 3, 1984, hasbeen disclaimed 3 Claims. (Cl. 260-29.6)

This invention relates to novel emulsion polymerized latices.

This application is a continuation-in-part of our copending applicationSer. No. 161,301, filed Dec. 21, 1961, and now abandoned.

The use of polymer latices such as latices of styrenebutadienecopolymers, polyvinyl acetate, acrylate ester polymers and the like inthe manufacture of water-based coating compositions is well known in theart. The common method of applying such coating compositions, e.g., bybrushing or rolling, requires that the coating compositions have asufiiciently high viscosity to enable its convenient transfer from thecontainer to the surface being painted. To attain the desired viscosity,thickening agents such as cellulose ethers and water-soluble gums arecustomarily added to the coating compositions. It is recognized in theart that the use of such thickening agents is not desirable, but to datetheir use has been a practical necessity to obtain desired viscosities.In particular, the more effective thickening agents customarilyernployed cause flocculation of the dispersed polymer and depend uponflocculation to increase the viscosity. As a result, the paint exhibitsrheology conducive to easy application, but sacrifices packagehomogeneity, leveling, gloss, bonding to chalked paint surfaces,exterior durability and film-thickness. Avoidance of flocculation isessen- "tial to obtain latex paints which will deposit glossy films.

In view of the foregoing, it obviously would be desirable to haveavailable to the art polymer latices which either have high viscositiesas prepared or whose viscosities can be increased significantly withoutadding thickeners v thereto.

It is an object of this invention to provide a novel emulsionpolymerized latex.

Another object of this invention is to provide a novel polymer latexwhich will thicken upon being adjusted to a pH on the basic side.

Other objects and advantages of the invention will be apparent from thefollowing detailed description thereof.

Briefly, the above and related objects are attained by polymerizingparticular monomer mixtures by particular emulsion polymerizationprocess steps. Specifically, monomer mixtures consisting of analpha,beta-ethylenically unsaturated carboxylic acid and at least onevinylidene monomer are polymerized in such a manner that the addition ofa specific amount of the carboxylic acid mono- Iner to thepolymerization reaction is delayed until at least about 70 Weightpercent of the total monomer mixture has been polymerized. The latex soproduced consists of polymer particles which have an inner polymercomposition with a polymer composition oriented to the surface of thepolymer particles and wherein the polymer composition oriented to thesurface contains the alpha,- beta-ethylenically unsaturated carboxylicacid. The latices, when adjusted to a pH of about 8-12, increasesignificantly in viscosity and films laid down therefrom are clear andglossy. When the latices are formulated with suitable pigments andrendered alkaline, coating compositions of brushalble and rollableconsistency are 3,401,134 Patented Sept. 10, 1968 An approximately 45%solids latex of an interpolymer of 48.5% styrene, 39% Z-methyl hexylacrylate, 6% acrylontrile and 6.5% methacrylic acid is prepared by amodification of the process described in Example Iof US. 2,767,153. Thefollowing solutions are prepared.

Kettle charge Component: Parts Water (distilled) 402 Triton X-l OO 1 1.7Triton X770 1.2 Tetrasodium pyrosphoate 0.2

Ethylene oxide condensate of nonylp'henol. 2 Sodium salt of an alkylaryl polyetlier sulfate.

Catalyst and emulsifier premix Component: Parts Water (distilled) 132Triton X- 0.5 Triton X-770 10.7 Potassium persulfate 2.7

Monomer charge I Component: Parts Acrylonitrile 24 Styrene 5'6 Monomercharge II Component: Parts Styrene 138 2-ethylhexyl acrylate Monomercharge 111 Component: Parts 2-ethylhexyl acrylate 31 Methacrylic acid 26The kettle charge is added to a glass-lined reaction vessel that isfitted with a reflux condenser and a stirrer and refluxed (atatmospheric pressure) for 15 minutes to deoxygenate the solution. Thereis then added to the reaction vessel 10 parts of the catalyst andemulsifier premix. The balance of the catalyst and emulsifier premix isadded to the reaction vessel at a uniform rate of 1.3 parts per minute,the total time of addition being 100 minutes. As soon as the initialaliquot of the catalyst and emulsifier premix is added to the reactionvessel, monomer charge I is added to the reaction vessel at a uniformrate of 2 parts per minute, the time of addition for this monomercharged being about 30 minutes. Immediately thereafter, monomer chargeII is added to the reaction vessel at a uniform rate of 5.5 parts perminute, the total time of addition of this monomer charge being about 50minutes. Immediately thereafter, monomer charge III is added to thereaction vessel at a uniform rate of 5' parts per minute, the additionof monomer charge III requiring approximately 10 minutes. Reflux iscontinued for an additional 15 minutes to polymerize the final traces ofmonomers. Reflux is then continued for an additional 15 minutes and 60parts of distillate are removed so as to remove by steam distillationany residual monomers present in the latex. The resulting latex issubsequently identified as Latex A.

The catalyst concentration and monomer addition times described in theparagraph above are selected so that the monomers polymerize atsubstantially the rate they are added to the reaction vessel. It will bespecifically noted that the acid monomer, i.e., methacrylic acid, is notintroduced into the polymerization reaction until approximately 85% ofthe total monomer charge has been polymerized. The amount of acid in thepolymer oriented to the surface of the particles so produced constitutesabout 45.5% of the polymer so oriented to the surface.

EXAMPLE II An approximately 45% solids latex of an interpolymer of 40.5%styrene, 49% of 2-ethylhexyl acrylate, 6% acrylonitrile and 4.5% ofmethacrylic acid is prepared by the emulsion polymerization reactionemployed in Example I except that the kettle and monomer charges are asfollows:

Kettle charge It will be specifically noted that the monomers s added tothe reaction kettle are added at such a rate that they polymerized at arate substantially equal to the rate at which they were added to thereaction vessel. It will be further noted that the acid, whichconstitutes 4 /2% of the total monomer charge is not added until about70% of the total monomer charge has been polymerized. The amount of acidin the polymer oriented to the surface of the particles so producedconstitutes about 15% thereof.

EXAMPLE III Example II is repeated except that in place of monomercharge HI of Example II the following monomer charge is employed:

Monomer charge III Component: Parts Z-ethylhexyl acrylate 24.5Methacrylic acid 5.5

It will be noted that the acid monomer which constitues 5 /2 of thetotal monomer charge is not added until about 70% of the total monomercharge is first polymerized. The amount of acid in the polymer orientedto the surface of the particles so produced constitutes about 18.3%thereof.

EXAMPLE IV The latices prepared in Examples I-III are diluted to 28%sol-ids. The viscosity of the samples is measured and found to be lessthan cps. The pH of the latices are then adjusted to about 9.0 withammonium hydroxide.

After standing for about 1 hour, the viscosities are measured again andare as follows:

Cps.

Example I 2000 Example II 10" Example III 2000 It will be noted that thelatex containing only 15% of acid in the polymer composition oriented tothe surface of the particles did not increase in viscosity when adjustedto a pH of about 9.0. The core contains of the monomer mixture.

This invention is directed to an emulsion polymerized latex of (A) analpha,beta-ethylenicaly unsaturated carboxylic acid and (B) at least onevinylidene monomer wherein the polymer particles comprise an innerpolymer composition with a particular polymer composition orineted tothe surface of the polymer particles. The polymer particles of the latexcan probably be visualized as having a shell-core configuration. Theinner polymer composition of the polymer particles of this inventionconsist of at least 70 and preferably 7 0-90 weight percent based on thetotal weight of the polymer particles of a polymer selected from thegroup consisting of homopolymers or interpolymers of at least onevinylidene monomer. The particular polymer composition oriented to thesurface of the polymer particles consist of an interpolymer of 18-75weight percent of (A) based on the weight of the oriented polymer withthe balance thereof being (B). Preferably, the acid monomer constitutes5.5-20 weight percent and more particularly 8-15 weight percent based onthe total weight of the polymer. Stated in another way, the acid monomerused in providing the polymer composition oriented to the surface of thepolymer particles preferably constitutes about 20- 65 weight percent andmore particularly about 25-50 weight percent based on the weightthereof. In the practice of this invention the polymer particles soprepared have a particle size of 0.01-1.0 and preferably 0.1- 0.5micron.

The critical feature of this invention is that the polymer compositionoriented to the surface of the polymer particles must contain theproportion of the carboxylic acid set forth above. It is this criticalfeature and the makeup of the polymer particles that provides the uniqueproperty of a latex increasing in viscosity containing these particleswhen the latex is adjusted to a pH of 8-12 and preferably 8.010. Thisunique property results in a latex which when applied to a surface orwhen com pounded with other ingredients provides a surface coatinghaving excellent gloss, excellent hideability and excellent applicationproperties.

In the practice of this invention, it is conceivable that the polymercomposition of the inner polymer can contain carboxylic acid. Thecritical feature is as stated above in that the polymer oriented to thesurface of the particles must contain 18-75 weight percent of carboxylicacid.

The acid monomers employed contain alpha,beta-ethy1- enic unsaturationand preferably a single carboxyl group. Typical examples of suchpreferred acid monomers are acrylic acid, methacrylic acid, crotonicacid, etc. Other acid monomers which can be employed include maleicacid, itaconic acid, and half esters of maleic acid and fumaric acidsuch as monomethyl maleate, monobutyl maleate, monododecyl maleate,monobutyl fumarate, etc.

The vinylidene monomers employed in the practice of this invention andwhich can be interpolymerized with the carboxylic acid monomer can beany vinylidene monomer as monoand di-olefins, e.g., ethylene, propylene,isobutylene, butadiene, isoprene, etc.', vinyl halides, e.g., vinylchloride, vinyl bromide, etc.; vinylidene halides, e.g., vinylidenechloride; esters of vinylidene monocar- 'boxylic acids with 118 carbonatom monohydric alcohols, e.g., methyl acrylate, methylalpha-chloroacrylate,

butyl acrylate, benzyl acrylate, dodecyl acrylate, thecorrespondingesters of methacrylic acid, etc.; amides and nitriles of vinylidenemonocarboxylic acids, e.g., acrylamide, methacrylamide, acrylonitrile,methacrylonitrile,

'etc.; vinylidene aromatic hydrocarbons and nuclear alkyl and halogenderivatives thereof, e.g., styrene, vinyl naphthalene,alpha-methylstyren'e, vinyl toluene, 2,4-dimethylstyrene, o, .m-,p-chlorostyrene, 2,5-dichlorostyrene, 2- methyl-4-chlorostyrene, etc.;vinyl esters of 1-18 carbon monocarboXylic acids such as vinyl acetate,vinyl stearate, and vinyl benzoate, etc. Diesters of maleic acid andfumaric acid with 1-18 carbon atom monohydric alcohols, while notvinylidene monomers in the strict sense of the word, can be usedinterchangeably therewith. Typical examples of such monomers are diethylmaleate, dibutyl fumarate, etc. In the practice of this invention,homopolymers and interpolymers of the above can be employed to preparethe inner polymer composition of the polymer particles. Preferably, theintelpolymer prepared herein to form the inner polymer composition ofthe polymer particles is selected from the group consisting ofhomopolymers and interpolymers of styrene wherein the interpolymerscontain at least 50 weight percent of styrene with the balance being anymonomeric compound which is interpolymerizable therewith.

In the broadest aspect of the invention, the acid monomer can bepolymerized with any vinylidene monomer or any mixture thereof set forthin the paragraph above to form the shell of the polymer particles.Preferably, however, the latices are prepared from monomers which willprovide polymers having second order transition temperatures not higherthan about 50 C. The selection of monomers meeting this requirement iswell within the skills of the art. Typical monomer compositions whichcan be employed to prepare the latices of the invention are set forthbelow:

(a) 80-95% methyl acrylate/5.5-20% acrylic and/r methacrylic acid,

(b) 80-95% butyl acrylate/5.5-% acrylic and/or methacrylic acid,

(0) -65% styrene/3-10% acrylonitrile/35-60% 2- ethylhexylacrylate/5.5-20% acrylic and/or methacrylic acid,

(d) 25-60% styrene/310% acrylonitrile/35-60% dibutyl fumarate/5.520%acrylic and/or methacrylic acid,

(6) 25-50% styrene/40% ethyl acrylate/5.5-20% acrylic and/ ormethacrylic acid,

(f) 25-60% methyl methacrylate/3-10% acrylonitrile/ -60% Z-ethylhexylacrylate/5.5-20% acrylic and/ or methacrylic acid,

(g) 80-95% vinyl acetate/5.5-20% acrylic and/or methacrylic acid,

(h) 8095% vinyl acetate/5.5-20% crotonic acid,

(i) 20-95% butadiene/O-75% styrene/5.5-20% acrylic and/ or methacrylicacid,

(j) 20-95% butadiene/O-75% acrylonitrile/5.5-20% acrylic and/ ormethacrylic acid,

(k) 20-95% butadiene/075% methyl methacrylate/ 55-20% acrylic and/ ormethacrylic acid,

(1) -75% vinyl chloride/ 15-55% vinyl acetate/5.5- 20% acrylic and/ ormethacrylic acid,

(In) 40-75% vinyl chloride/l5-55% ethyl acrylate/ -20% acrylic and/ ormethacrylic acid,

(n) 40-75% vinyl chloride/ 15-55% dibutyl fumarate/ 55-20% acrylic and/or methacrylic acid.

The monomers can be polymerized by any of the known emulsionpolymerization processes provided only that the addition of a specificweight percent of the carboxylic acid monomer to the polymerizationreaction is delayed until at least about 70 weight percent of the totalmonomers have polymerized. Of necessity, the monomers are charged to thepolymerization reaction in two or more separate monomer charges. In thepreferred embodiment of the invention, the vinylidene monomers, whichconstitute 70-90 weight percent of the total monomers are emulsimonomerswill polymerize.

In preparing latices from monomers of two ormore vinylidene monomers,one of which normally gives polymers having a high second ordertransition temperature (e.g., styrene, acrylonitrile or methylmethacrylate) and one of which normally gives polymers having a lowsecond order transition temperature (e.g., an alkyl acrylate, a dialkylmaleate or adialkyl fumarate), it is preferred to employ a specialmodification of the continuous monomer addition process. Specifically,the vinylidene monomer giving polymers of high second order transitiontemperature should be charged first, followed by the vinylidene monomergiving polymers of low second order transition temperature and finallyby the acid monomer. Example I illustrates this embodiment of theinvention. Pigmented coating compositions prepared from such laticesoffer an optimum combination of ease of application, quick drying andfilm-durability.

The emulsifying agents, polymerization initiators, polymerizationmodifiers, etc., that are employed in the polymerization process of thepresent invention are those commonly used in known prior art emulsionpolymerization processes.

The latices of the present invention differ from prior art latices ofpolymers prepared from identical monomer mixtures primarily indeveloping unusually high viscosities at pH values in the range of 8-12and preferably 8-10. The freeze-thaw stability of the latices of theinvention is also outstanding. Other properties of the latices and thefilms prepared thereby are in general similar to those which would bepredicted from the monomer composition of the interpolymer solids.

The latices of the invention, particularly when adjusted to a pH ofabout 8-12 and preferably 8-10, have a much higher viscosity thanconventional prior art latices. The high viscosities of these laticesmake them particularly suitable for coating and/ or impregnatingapplications such as coating paper, impregnating glass fiber mats, etc.

In rendering the latices alkaline to increase their viscosity, it ispossible to use permanent. alkalies such as sodium carbonate, sodiumhydroxide, etc. Preferably, however, volatile nitrogenous bases shouldbe used for this purpose. Examples of such bases include ammonia andamines having atmospheric boiling points not higher than about C., e.g.,mono-, diand tri-methylamines, propylamine, ethanolamine,isopropanolamine, etc.

To prepare the protective coating compositions of the invention, thelatices of the invention will be adjusted to a pH of about 8-12 and willhave dispersed therein pigments of the type customarily employed in theformulation of latex-based coating compositions. Typical examples ofsuch pigments include clay, magnesium, silicate, iron oxide, bariumsulfate, titanium dioxide, phthalocyanine blue, etc. Carbonate pigmentssuch as calcium carbonate can under some conditions of storage reactwith the carboxyl groups of the latex and, consequently, preferablyshould not be included in the coating compositions. The coatingcompositions of this invention, however, because of their highviscosity, do not require the addition of the customarily usedthickeners such as cellulosic ethers, water-soluble gums, etc. By theproper selection of the type and quantity of pigments, it is possible toprepare coating compositions which dry to form fiat, semiglossy and/orglossy films. Multi-component coating compositions which contain a latexof this invention as one component dry to form exceptionally hard anddurable films. Such compositions are disclosed and claimed in copendingapplication Ser. No. 166,368, filed Ian. 15, 1962,

now abandoned, and assigned to the assignee of the present application.If desired, the coating compositions of the invention can be formulatedto include therein additional film-forming components such asconventional latices, oil-modified alkyd resins, drying oils, etc.

The coating compositions of this invention can be applied byconventional techniques to protect metal, e.g., steel, copper andaluminum, plaster, wooden, plastic and like surfaces.

The above descriptions and particularly the examples are set forth forpurposes of illustration only. Many variations and modifications thereofwill be apparent to those skilled in the art and can be made withoutdeparting from the spirit and scope of the invention herein described.

What is claimed is:

1. An aqueous latex prepared by the aqueous emulsion polymerization of amonomer mixture of (A) from about 5.5 to 20 percent by weight of analpha,beta-ethylenically unsaturated carboxylic acid and (B) at leastone vinylidene monomer which is interpolymerizable therewith, in whichpolymerization the addition of at least a portion of the acid monomer tothe emulsion is delayed until at least 70 percent by weight of the totalWeight of monomers have polymerized; said acid monomer constituting from18 to 75 percent by weight of the remaining monomers so added to theemulsion; said polymer particles having an average particle size of from0.01 to 1.0 micron.

2. An aqueous latex as in claim 1 'wherein the acid monomer is selectedfrom the group consisting of acrylic acid, methacrylic acid, andmixtures thereof.

3. An aqueous latex as in claim 1 wherein (B) is at least 50 percent byweight styrene based on total monomers (B).

References Cited UNITED STATES PATENTS 2,767,153 10/1956 Sutton 26029.62,859,201 11/1958 Uraneck et al. 260-297 2,962,465 11/1960 Lindstrom etal. 260-296 3,073,791 1/1963 Barkhuit 260-296 3,296,175 1/1967 Fantl eta1 26029.6

FOREIGN PATENTS 233,298 3/ 1961 Australia.

DONALD E. CZAJA, Primary Examiner.

R. W. GRIFFIN, Assistant Examiner.

1. AN AQUEOUS LATEX PREPARED BY THE AQUEOUS EMULSION POLYMERIZATION OF AMONOMER MIXTURE OF (A) FROM ABOUT 5.5 TO 20 PERCENT BY WEIGHT OF ANALPHA,BETA-ETHYLENICALLY UNSATURATED CARBOXYLIC ACID AND (B) AT LEASTONE VINYLIDENE MONOMER WHICH IS INTERPOLYMERIZABLE THEREWITH, IN WHICHPOLYMERIZATION THE ADDITION OF AT LEAST A PORTION OF THE ACID MONOMER TOTHE EMULSION IS DELAYED UNTIL AT LEAST 70 PERCENT BY WEIGHT OF THE TOTALWEIGHT OF MONOMERS HAVE POLYMERIZED; SAID ACID MONOMER CONSTITUTING FROM18 TO 75 PERCENT BY WEIGHT OF THE REMAINING MONOMERS SO ADDED TO THEEMULSION; SAID POLYMER PARTICLES HAVING AN AVERAGE PARTICLE SIZE OF FROM0.01 TO 1.0 MICRON.